When species are listed as threatened or endangered, the habitats or ecosystems upon which they depend are described. The Service must, in most cases, officially designate specific areas as critical habitat for a species when listing it under the Endangered Species Act.
Federal agencies must insure that any action they authorize, fund, or carry out is not likely to result in habitat destruction or adverse modification of the designated areas.
The Service, acting for the Secretary of the Interior, can designate habitat of listed species which is considered "critical" to the species survival and recovery. This geographic area contains those physical or biological features considered essential for the conservation of the species that may require special management or protections.